The present invention is related to planar broadband array antennas and, more particularly, to controlled radiation pattern array antennas.
Controlled Radiation Pattern Antennas (CRPA) are known in the art. A CRPA operates by using spatial filtering techniques to steer nulls in the antenna radiation pattern towards sources of interference. A CRPA is normally an array antenna comprised of a plurality of antenna elements. By controlling the phase gradients between antenna elements, the radiation pattern of the antenna can be controlled.
In prior art implementations of controlled radiation pattern atnennas, stacked patch dipole antennas are used as the array elements. U.S Pat. No. 5,955,987, granted to Murphy, et al, for example, discloses a CRPA antenna using three dipole antenna patches. U.S. Pat. No. 6,052,086, granted to Kudoh discloses an array antenna having a plurality of dipole patches on one side of a baseboard.
A four element controlled radiation pattern antenna using stacked patch dipole antennas is described in xe2x80x9cCharacterizing the Effects of Mutual Coupling on the Performance of Miniaturized GPS Adaptive Antenna Arrayxe2x80x9d by Basrur Rao et al, ION GPS 2000, pages 2491-2498.
It is often desirable to be able to mount a controlled radiation pattern antenna on a vehicle. Many receivers for the global positioning system (GPS) utilize controlled radiation pattern antennas to reduce the effects of multipath or other interfering signals. However, many CRPAs are physically too large to fit within given form factors required by the host vehicle. Reduction in size of the antenna is possible, but this reduction in size brings the antenna elements closer together, thereby causing an increase in mutual coupling, which can negatively affect the performance of the array.
While the art describes controlled radiation pattern antennas, there remains a need for improvements that offer advantages and capabilities not found in presently available devices. Specifically, CRPA antennas are often larger than is desirable. Additionally, mutual coupling between adjacent antenna elements often reduces the performance of the antenna.
There is needed a CRPA antenna that can be made physically smaller, and there is a further need to reduce mutual coupling between adjacent antenna elements to improve antenna performance.
A controlled radiation pattern array antenna uses spiral slot array elements. The antenna comprises a substantially planar dielectric substrate having a first surface and a second surface. A conductive layer having a plurality of similar curved slotted openings is disposed on the first surface. The curved slotted openings form a plurality of spiral slot array antennas. The spiral slot array antennas are located such that the angle "PHgr" between any two adjacent spiral slot array antennas with respect to the center of the antenna is equal to 2xcfx80/N, wherein N is the number of spiral slot array antennas.
A plurality of transmission lines is disposed on the second surface of the antenna with each transmission line being aligned with a corresponding spiral slot array antenna on the first surface. Each antenna element comprising of the spiral slot array and the transmission line located underneath is rotated about its center such that adjacent antenna elements are rotated by 2xcfx80/N with respect to each other. The rotation of 2xcfx80/N between adjacent elements randomizes the pattern error of each individual element yielding a very uniform radiation pattern of a combined array of all antenna elements.